1. Field of the Invention
The present invention relates to a color indication comparison method for indicating the color position relationship of two colors.
2. Description of the Prior Art
Heretofore, color indication methods have been established in "JIS Z 8722 Substance Color Measuring Method" for the system of three stimulus values XYZ and "JIS Z 8730 Color Difference Indication Method" for indicating the color difference between two colors.
The conventional system of color representation employed in those established methods describes a color as a point in a three-dimensional space. The prior art is described herein using the L*a*b color indication system by way of example, but the same method is employed also in other systems of color representation.
FIG. 1 shows orthogonal coordinations with the abscissa representing an a* value and the ordinate representing the b* value, and which together correspond to a planar chromaticity diagram in the form of a space of equal color difference. If the a* and b* values of a color to be indicated are determined, these values are plotted on FIG. 1 as the abscissa and ordinate values, respectively, to indicate the position of the color.
R.sub.1 (red), G.sub.1 (green), and B.sub.1 (blue) are plotted as examples of indications of specific colors.
Ten hues (red, yellowish red, yellowish green, green, bluish green, blue, bluish purple, purple, and purplish red) depicted on the outer circle represent approximate positions of colors corresponding to the respective hues. A line 2 connected between each of such positions and the origin 0 are equal hue lines OH, OH.sub.2, and OH.sub.3 indicative of the corresponding equal hue.
In the past, therefore, a planar chromaticity diagram including the names of the ten hues depicted thereon as shown in FIG. 1 was prepared in advance, L*, a*, and b* values were calculated from the measured XYZ values for a particular color using conventional calculations, and they were plotted on FIG. 1 to obtain the coordinate position of the relevant color.
However, when two colors are located adjacent to each other, it is often difficult to make clear the relationship between those two colors.
While the planar chromaticity diagram 1 shown in FIG. 1 has coordinates for representing all ranges of colors, it is required in many cases to compare and determine a color deviation between two colors which cannot be appreciated at a glance. Thus, even if those two colors are plotted on the chromaticity planar diagram of FIG. 1, they are located too close to each other to practically distinguish between them.
Further, colors are essential elements for all types of industrial products and materials, and have vital importance particularly in the fields of paint, plastics, dyes, printing ink, etc. When handling colors in these fields, it is often required to find the color position relationship of two colors in order to determine, for example, in which direction a finished color deviates from a specific color, or in which direction the color has been changed due to the passage of time. The prior art has had difficulties in precisely finding such relationships.
For this reason, there has been a strong demand to develop a color indication comparison method which can distinguish a color deviation between two colors, even if the two colors to be compared differ by a very small color difference.